Data display device of the gas discharge type

ABSTRACT

A gas discharge type data display device is formed of a stack of alternately conductive and insulating elements for localizing the discharge by proper potential distribution, the control of which is effected by a conductive screen electrode positioned between anode and cathode. Discharge is confined in a plurality of cavities provided in said stack. The device permits a storage of data in said cavities for an indefinite period of time.

I United States Patent [191 [1 1 3,735,38 Coulon May 22, 1973 [5 DATA DISPLAY DEVICE OF THE GAS R erences (Iited DISCHARGE TYPE UNITED STATES PATENTS lnvemo" Maurie? Comm, Paris fiance 3,559,190 1 1971 Bimr et a1. ..313/109.s x Assigneez ThomsomCsF Paris, France 3,641,383 2/1972 Tagawa ..3l3/ 109.5 [22] Filed: Sept. 22, 1971 Primary Examiner-Roy Lake Assistant Examiner-Siegfried H. Grimm P 182,763 Attorney-Edwin E. Greigg [30] Foreign Application Priority Data [57] ABSTRACT A gas discharge type data display device is formed of a Sept. 24, 1970 France ..70/34663 Stack of alternately conductive and insulating ele ments for localizing the discharge by proper potential [52] 1.8. CI ..3l3/109.5, 313/193 distribution the control of which is effected by a Cl J' 61/66 7/04 ductive screen electrode positioned between anode [58] Field of Search ..313/l09.5, 193, 195;

'3 15/84.6, 169 R, 169 TV; 340/324 R and cathode. Discharge is confined in a plurality of cavities provided in said stack. The device permits a storage of data in said cavities for an indefinite period of time.

4 Claims, 5 Drawing Figures Patented May 22, 1973 2 Sheets-Sheet 1 Patented May 22, 1973 3,735,180

2 Sheets-Sheet 2 DATA DTSPLAY DEVICE OF THE GAS DISCHARGE TYPE This invention relates to display devices which operate by means of an electrical discharge in a gas and which, by virtue of segments or dot matrices, can produce a visual display of data such as letters, digits, signs, characters, symbols and linear profiles of all kinds. The segments or dots constitute the elementary visual units in said display.

In devices of this kind, the elementary visual units are located inside an enclosure into which, after having produced a vacuum there, there is introduced a gas under a certain pressure, generally a rare gas or a mixture of several such gases, or, possibly, mercury vapor.

ln devices wherein the visual units are constituted by conductor segments insulated from one another, the cold cathodes forming these segments are surrounded, in operation, by a light halo produced in their immediate vicinity by ionization of the gas when an appropriate voltage is applied to the common anode of the tube.

To this end, the anode is connected to the positive terminal of a DC. supply, while each cathode segment is connected, through a switch, to the negative terminal of said supply. Depending upon the data which is to be displayed, voltage is applied to these cathodes in accordance with a given program for operating the switches. The simultaneous display of several segments provides a complete display at the source.

In those devices in which said units are dots in a dot matrix, the display is achieved, again by gas ionization, by means of a matrix of insulating material provided with holes filled with said gas and located between two networks of generally rectilinear transparent electrodes which cross one another over said holes. A suitable voltage is applied between said electrodes in order to achieve selective illumination of the various holes, the illuminated entirety of which defines in the form of dots the sign which is to be displayed.

In both these cases, the discharge at the unit is said to be piloted or, more briefly, it may be stated that the unit is piloted.

If it is desired to maintain a data bit and in order to achieve repeated lighting up of the segments or dots, repeated application of voltage to the aforesaid segments or dots is effected at a certain frequency for this purpose. Such activity is referred to as refreshing the data.

If it is desired to pilot a large number of units, it is apparent that it is desirable to utilize only one decoder for the assembly of display devices which constitute the display panel. In this case, the decoder is switched successively to each unit. The duration of display time assigned under these circumstances to each unit is inversely proportionate to the number of units. Moreover, the frequency with which the data are refreshed should take account of the retinal persistance of the human eye in order to avoid flicker and should therefore not be less than 30 cycles per second.

These two essentials impose two major requirements:

1. The active data-processing memory, which is the origin of the data to be displayed and is integrated into the equipment of which the aforesaid display devices form part, should be available for the whole duration of the display time;

2. The unit should be capable of handling a low operating ratio, that is, it should have a substantial dynamic range of light emission. Accordingly, taking into account the permissible power levels in the existing devices, a ratio of between one-tenth and one-twentieth is a minimum.

The device in accordance with the invention is not bound by these two requirements. It has an intrinsic memory which thus enables data to be stored indefinitely and thus makes it unnecessary to perform the data refreshing operation. Under these circumstances, the number of units piloted by a single decoder circuit can be considerably increased without being limited by the aforesaid considerations of flicker and brightness.

The data display device forming the subject of the present invention, which operates by the ionization of a gas inside an envelope and comprises at least one anode and a plurality of cathodes, incorporates a structure formed of stacked, alternating conductor and insulator elements, in order to localize the discharge at the level of each cathode by an appropriate distribution of the potentials.

The control of this distribution is effected by the addition of a screen electrode disposed between thecathodes and the anode, and by the shape of a straight section of the volume in which said discharge is confined. To this end, the screen electrode and the interspersed insulating elements, are provided with openings. Once in position, the assembly delimits around the cathodes as many elementary volumes or cavities electrically isolated from one another, as there are units to be piloted. Thus, in operation, in each of these cavities, there is confined an elementary discharge representative of the corresponding unit. It has been found that under these conditions, in each elementary volume, a suitable bias applied to the screen electrode gives a special discharge characteristic to the cathode-anode assembly of the unit. In other words, if, in an unconfined volume, the triggering voltage Va is for example volts, using the arrangements in accordance with the invention, under identical conditions, that is to say with electrodes of the same kind, the same filler gas, the same cathode- I anode interval etc., a markedly higher voltage, for example 155 volts is obtained. The magnitude of this voltage is a function of the selected geometry and the bias voltage applied to the screen electrode.

It has likewise been observed that once the discharge is achieved, it is necessary to reduce the anode voltage to a level close to the normal extinction voltage, for example 132 volts, in order to block it. Consequently,-

there is a fork between the striking voltage and the extinction voltage (this fork is in the order of 20 volts in the present instance), within which, depending upon the direction of course of the voltage-current characteristic pertaining to the device, two stable states can exist: extinguished" and illuminated." By applying 10 volt pulses of short duration (approximately 200 microseconds) to the cathodes (or +pulses to the anode) with a constant anode bias of volts, it is possible to cause a transition from the extinguished state to the illuminated state. The device thus has memory properties. i

The invention will be better understood from a consideration of the ensuing description and the attached drawings given here by way of non-limitative example, in which:

FIG. 1 is an exploded isometric view illustrating the component elements of one embodiment of the device in accordance with the invention;

FIG. 2 is a sectional side elevational view of the same embodiment in an assembled condition;

FIG. 3 is an exploded isometric view illustrating the component elements forming a part of another embodi' ment of the device in accordance with the invention;

FIG. 4 is a sectional side elevational view of the part shown in FIG. 3 and FIG. illustrates the voltage-current characteristic of a device in accordance with the invention.

FIGS. 1 and 2 relate to the display devices in which the elementary units to be displayed are constituted by segments. The component 1, made of glass or a glassmetal bonded structure, constitutes a conventional base of the type used in electron tube technology and serves as the carrier for the assembly of electrodes in such a tube. Through the insulating glass portions of the base 1 there extend supply leads 2 for the assembly of electrodes of said device as well as a certain number of posts 3 which will be referred to later as the specification progresses.

The cathodes 4 are solid metal segments. These cathodes define the shape of the sign which is to be displayed by the device in accordance with the invention. These segments number seven in the present example and are distributed in a conventional way to enable any digit and a certain number of letters of the alphabet, to be displayed.

The plate 5 which is made of a refractory insulating material, for example mica or alumina, is provided with openings 5a in a pattern identical to that presented by the entirety of segments 4. The lengths and widths of the openings, however, are slightly larger than the dimensions of said segments so that when the plate 5 has been placed upon the base 1, said openings 5a circumscribe the segments 4. In addition, since the thickness of the plate 5 is appreciably greater than the of the segments 4, the latter are necessarily recessed in the interior of the openings 5a.

A metal plate 6, which is placed on the insulating plate 5, constitutes the screen electrode whose function has been set forth earlier. On the metal plate 6 there are stacked an insulating plate 7 and another metal plate 8 which is the anode. These three plates 6, 7 and 8, contain openings 6a, 7a, 8a which, similarly to the openings 5a in plate 5, are arranged in registry with the segments 4.

As described in French Patent Application No. PV. 70.1 1,704 filed on Apr. 1, 1970, the assembly of plates 5, 6, 7 and 8 stacked on the base 1 defines above and about each segment 4 a cavity 10 in which the discharge is confined. The discharges which occur about each of the cathode segments 4 are thus limited to spaces which are isolated from one another. In each of the cavities 10 the screen electrode 6 exercises the control function hereinbefore described.

The dimensions of the openings 5a, 6a, 7a, 8a differ slightly from one another. Thus, the insulating plates 5 and 7 have openings 5a and 7a which are shorter in length and width than the openings (in and 8a in the conductive plates 6 and 8. This geometry of the openings is determined experimentally in order to achieve control of the distribution of the discharge within the cavities 10 not only by the action of the screen electrode but, as explained hereinbefore, by means of the shape of the straight section of the volume or cavity in which the discharge is confined. In addition, this kind of arrangement makes it possible to protect the top part of said insulating plates, opposite said conductive plates, against cathode spluttering to thus avoid any leakage conductance between the electrodes 4, 6 and 8.

The posts 3 align the assembly of plates 5, 6, 7 and 8 and help to position associated elements such as getters, gas-release or mercury-release capsules, etc., which are conventionally incorporated into devices of this kind but which, for preserving clarity, are not shown in the figures.

After stacking the plates 5, 6, 7 and 8 on the base 1 in the indicated order, the plate assembly is secured to the base by known means applied to the posts 3, for example eyelets, pinched-out lugs, etc. Such securing means, not shown, are well known in the technique of assembling electronic tubes.

One method of energizing the device is as followsi The segments 4 which function as cathodes, are grounded.

The electrode 8 which is the anode, is placed at a constant potential, for example, for a given geometry, 160 volts.

The screen electrode 6 is placed at a positive potential of a value that is between the cathode and the anode potential so that there is no discharge between cathodes and anode. Thus, the potential applied to the screen electrode 6 may be for example volts, so that a short negative pulse in the order of 10 volts, applied to those of the cathodes which are to be piloted, brings about the triggering of the discharge in the aforesaid manner. The discharge is maintained indefinitely after said cathodes have reverted to ground potential.

A modulation of 10 volts applied to the anode simultaneously with the command pulse, cancels the recording command if required, without affecting the states of the adjoining segments. Likewise, commands can be selected by simultaneously applying a -5 volt pulse to the selected cathode and a +5 volt pulse to the anode. It is thus possible to multiplex several units by driving all the cathodes and the anode of the unit selected.

The extinction of the discharge over the whole of the unit is effected by applying a 20 volt pulse to the anode.

FIGS. 3 and 4 relate to display devices in which dots in a dot matrix constitute the elementary units. In this instance, the control is effected by an XY coordinate addressing system.

In FIGS. 3 and 4 the electrodes 14 group together a certain number of such dots in columns. The dots of one column are electrically interconnected. By energizing one line and one column, the electrodes 18 select from these dots the ones which are to be controlled. The component 16 is the screen electrode.

As in the precedingly described embodiment, the discharges corresponding to the various dots are confined to the interior of the cavities 20, the geometry of which is similar to that of the cavities 10 in the first embodiment. The plates 15 and 17 are interposed insulating plates similar to plates 5 and 7 of the first embodiment according to FIGS. 1 and 2. The display device according to the embodiment shown in FIGS. 3 and 4 can be extended as desired to form a display bar, the length of which is limited only by technological considerations. The bar according to FIGS. 3 and 4 comprises, similarly to the first embodiment, a base 11, supply leads 12, centering posts 13 and an envelope 19 which is sealed to the base 11.

The manner of operation at each of the units, constituted by dots in this embodiment, is identical to that described in connection with FIGS. 1 and 2.

In the case of a logic system generating positive pulses, such as MOS integrated circuits, the devices described, whether of the segment or dot type, can be energized in a different fashion. In such a case the grounded electrodes 4 or 14 function as anodes. The electrode 8 or 18 functioning as the cathode, is placed at a negative potential, for example -160 volts for a given geometry. The electrode 6 or 16, functioning as the screen, is placed at the intermediate potential of l volts for example, in order to block the discharge between cathode and anode in a manner described earlier. The conditions of operation remain the same as in the aforedescribed circuit except that this time positive pulses are used.

By using the aforedescribed mechanical arrangements and distributions of potential, it is possible to create all the currently employed forms and patterns as well as types of input.

A multiple display device operating in the above described manner can then be designed as conventional multilayer printed circuits wherein the electrodes are disposed at the surface and the leads between corresponding segments are insulated from one another.

The composite circuit thus obtained supports the stack of electrodes and insulators described in connection with FIGS. 1, 2, 3 and 4. A transparent envelope is likewise sealed to the bar thus formed.

It is to be understood that numerous variants may be constructed in the framework of the technology of assembly of the display devices illustrated, without departing from the scope of the invention. In particular for convenience of connection to circuits, the leads 2 of the segments 4 in FIGS. 1 and 2 can be taken out from the side of the base, rather than causing them to pass through the base 1.

FIG. 5 illustrates the volt-ampere characteristics relating to one elementary cell.

Starting with a low and increasing voltage, the current remains neglible up to the triggering voltage Va. At that point the current suddenly assumes the value which corresponds to the ordinate of point A and varies thereafter following an arc AC. From the point C and for decreasing voltages the current decreases following the curve CA, but is maintained until the point B, the abscissa Ve of which represents the extinguishing voltage. At that point and for smaller voltages the current again becomes neglible.

The afore-described cycle, the course of which is indicated by arrows in FIG. 5, thus represents a hysteresis characterized by the area of the quadrangle Ve, Va, A, E. The voltages between Va and Ve correspond to metastable operational points of the discharge. Thus, the discharge is and remains established if the triggering voltage Va has been previously exceeded. The discharge is not established and is not initiated if previously the voltage has been lowered below the value of Ve. The quadrangle Ve, Va, A, E thus bounds the domain in which there exists the memory phenomenon of the device forming part of the invention.

The structure forming the subject of the invention is adaptable to all the known forms of display; its application therefore extends to any known form of illuminated data display, in particular the display in one plane of arbitrary linear profiles by means of a dot matrix.

The three essential advantages of these devices are: D.C. supply;

low-amplitude pulse control adapted to be utilized with all the logic systems currently industrially developed; this control is compatible in particular with integrated circuits which combine the complex functions of multiplexing, code conversion and control, whatever the polarity involved;

data read-out without erasing due to the memory integrated into the device which makes possible the storage of a large number of data items which do not require refreshment or restoration of their brightness.

This local memory is fully exploited whenever data requires distribution to several users or storing for a substantial period of time. It makes possible a more efficient use of active data processing memories which originate the information to be displayed, and in some applications makes it unnecessary to provide a supplemental refresher memory.

What is claimed is:

1. In a data display device of the gas discharge type, the combination comprising A. at least one anode,

B. a plurality of cathodes separated from one another and from said anode,

-C. means for applying voltages separately to each cathode,

D. means defining a plurality of cavities, each containing one of said cathodes for confining the discharge within as many independent volumes as there are cathodes and E. means disposed between said cathodes on the one hand and said anode on the other hand for forming, together with said cathodes and said anode, an intrinsic memory in said device to store data therein for an indefinite period of time, said last-named means including 1. a screen electrode and 2. insulating elements disposed between said cathodes and said screen electrode and between said screen electrode and said anode.

2. An improvement as defined in claim 1, wherein said anode and said screen electrode are formed as metal plates positioned over the plurality of said cathodes in a superposed relationship, said insulating elements are constituted by a first insulator plate disposed between said cathodes and said screen electrode and by a second insulator plate disposed between said screen electrode and said anode, each metal plate and each insulator plate is provided with a plurality of openings in an arrangement and configuration corresponding to those of said cathodes, the openings in different plates are in alignment to define said cavities.

3. An improvement as defined in claim 2, wherein the openings in said insulator plates have a straight section smaller than the straight section of the corresponding openings in said metal plates.

4. An improvement as defined in claim 2, wherein said insulator plates are made of a refractory material. i i 

1. In a data display device of the gas discharge type, the combination comprising A. at least one anode, B. a plurality of cathodes separated from one another and from said anode, C. means for applying voltages separately to each cathode, D. means defining a plurality of cavities, each containing one of said cathodes for confining the discharge within as many independent volumes as there are cathodes and E. means disposed between said cathodes on the one hand and said anode on the other hand for forming, together with said cathodes and said anode, an intrinsic memory in said device to store data therein for an indefinIte period of time, said lastnamed means including
 1. a screen electrode and
 2. insulating elements disposed between said cathodes and said screen electrode and between said screen electrode and said anode.
 2. insulating elements disposed between said cathodes and said screen electrode and between said screen electrode and said anode.
 2. An improvement as defined in claim 1, wherein said anode and said screen electrode are formed as metal plates positioned over the plurality of said cathodes in a superposed relationship, said insulating elements are constituted by a first insulator plate disposed between said cathodes and said screen electrode and by a second insulator plate disposed between said screen electrode and said anode, each metal plate and each insulator plate is provided with a plurality of openings in an arrangement and configuration corresponding to those of said cathodes, the openings in different plates are in alignment to define said cavities.
 3. An improvement as defined in claim 2, wherein the openings in said insulator plates have a straight section smaller than the straight section of the corresponding openings in said metal plates.
 4. An improvement as defined in claim 2, wherein said insulator plates are made of a refractory material. 